While Obama carried the state in the general election by a comfortable margin that year, polls this year have shown voters narrowly preferring Romney, who plans to wage his own major effort in Iowa.
Obama pointedly chose the same turf where Romney, the presumptive Republican nominee, once declared that corporations are people. Obama said Romney would roll back regulations and return to policies that he said helped create the recession and would increase government deficits.
Last week, Romney said Obama had created "a prairie fire of debt." On Thursday, Obama said Romney's tax plan is "like trying to put out a prairie fire with some gasoline."
In a statement issued after the speech, Romney spokesman Ryan Williams said: "A president who broke his promise to cut the deficit in half by the end of his first term has no standing when it comes to fiscal responsibility."
Obama's visit to Iowa underscored his vulnerability with working-class voters and his effort to identify with the middle class.
Earlier, in blue-collar Newton, Iowa, once the prosperous headquarters of the appliance manufacturer Maytag Corp., Obama visited a wind-turbine plant to push his alternative-energy agenda and delivered a message that could as well have applied to all of Iowa. "Yeah, we're facing tough times, but we're getting through them, we're getting though them together," he said.
While Iowa offers only six of the 270 electoral votes needed to win the presidency, how its voters ultimately judge Obama is expected to be an important factor in the race.
"Last time it was a lot more exciting. It was a new thing," said Nancy Bobo, a Des Moines Obama volunteer and one of his earliest Iowa backers in 2008. "Today, we're all just very serious."
Obama has struggled to attract blue-collar voters, keys to winning struggling swing working-class regions such as southeast Ohio, Western Pennsylvania and rural Iowa. Newton is the seat of Iowa's Jasper County, where unemployment was 7.1 percent in April, higher than Iowa's average but down sharply from last winter.
The state shows a candidate's ability to win support in the heartland. It could help Romney in his effort to peel back states Obama won in 2008, or help Obama put Romney away.
Obama has already spent more than $2.6 million on advertising, a pace as aggressive as in any other battleground state. He has been a regular visitor, and was making his second trip in a month.